In the semiconductor processes, there is often a need for etching a material layer in a lateral direction, while not etching it in a vertical direction. Here, so called “lateral direction” means a direction substantially parallel to a substrate surface, and so called “vertical direction” means a direction substantially vertical to the substrate surface. FIG. 1 shows an example. As shown in FIG. 1, on a substrate 100 there is a feature 101 formed, which protrudes with respect to the substrate surface. The protruding structure 101 may be integral with the substrate 100 (as with the example shown in FIG. 1), or alternatively may be a different layer from the substrate 100 (not shown). Such an arrangement where a protruding structure is formed on a substrate is common in the semiconductor field. For example, a Fin Field Effect Transistor (FinFET) has a protruding fin formed on a substrate. Usually, a material layer 102 needs to be formed on both sides of the protruding structure 101 on the substrate 100. For example, in the situation of the FinFET, usually an isolation layer needs to be formed on both sides of the fin.
Conventionally, to form the material layer 102 on both sides of the protruding structure 101, a layer of material constituting the material layer 102 may be deposited on the substrate 100 (including the protruding structure 101), and then patterned to form the material layer 102. If there is an effective way to laterally etching the deposited layer to remove the material on side walls of the protruding structure 101, with no or very little etching in the vertical direction, the arrangement shown in FIG. 1 where the material layer 102 is formed on both sides of the protruding structure 101 on the substrate 100 will be achieved.
Unfortunately, there is no such an effective way of lateral etching yet. In the prior art, the arrangement shown in FIG. 1 is manufactured generally as follows. Specifically, as shown in FIG. 2(a), firstly a layer (102′) of material constituting the material layer 102 is deposited on the substrate 100 (including the protruding structure 101). During the deposition, process parameters can be controlled so that the deposited layer 102′ has a relatively large thickness in its portions extending in the lateral direction (i.e., portions positioned on the substrate 100) and a relatively small thickness in its portions extending in the vertical portion (i.e., portions positioned on the side walls of the protruding structure 101). Then, as shown in FIG. 2(b), the deposited layer 102′ is isotropically etched to remove the portions of the deposited layer 102′ on the side walls of the protruding structure 101. The portions of the deposited layer on the substrate 100 are left to some extent after the isotropic etching due to their relatively large thickness. Here, the material layer 102 may still remain on top of the protruding structure 101 (not shown in FIG. 2(b)).
However, there may be the following problems in the prior art. First, to deposit a material layer which is relatively thick in its portions extending in the lateral direction while relatively thin in its portions extending in the vertical direction causes a great challenge to the deposit process. Second, there is no effective control on etching in the lateral direction and the vertical direction.
In view of the above problems, there is a need for a method of controlled lateral etching.